1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same. For example, the zoom lens is suitable for an image pickup apparatus, such as a video camera, an electronic still camera, a broadcasting camera, and a monitoring camera, which uses a solid-state image sensor, or an image pickup apparatus such as a camera which uses a silver-halide film.
2. Description of the Related Art
In recent years, there have been remarkable advances in the function of an image pickup apparatus, such as a video camera, a digital still camera, a broadcasting camera, and a monitoring camera, which uses a solid-state image sensor and in the function of a camera which uses a silver-halide film. Therefore, as a photographic optical system used therein, there has been a demand for a zoom lens having a high zoom ratio (a high magnification variation ratio) and a high resolution over the entire zoom range. As a zoom lens satisfying such a demand, there is known a positive lead type zoom lens that includes the following in order from an object side to an image side: first, second, and third lens units respectively having positive refractive power, negative refractive power, and positive or negative refractive power, and a rear lens group having one or more lens units subsequent thereto.
As the positive lead type zoom lens, there is known a zoom lens that includes four lens units respectively having positive refractive power, negative refractive power, positive refractive power, and positive refractive power in order from an object side to an image side (U.S. Pat. No. 7,206,137). Further, there is known a zoom lens that includes five lens units respectively having positive refractive power, negative refractive power, negative refractive power, positive refractive power, and positive refractive power in order from an object side to an image side (U.S. Pat. No. 6,278,559 and U.S. Pat. No. 7,672,062). Still further, there is known a zoom lens that includes five lens units respectively having positive refractive power, negative refractive power, positive refractive power, negative refractive power, and positive refractive power in order from an object side to an image side (U.S. Pat. No. 7,864,443).
U.S. Pat. No. 6,278,559 discusses a high-performance zoom lens that uses a glass material having a high refractive index and comparatively a low dispersion to form a negative lens of a second lens unit so that chromatic aberration, curvature of field, and astigmatism are satisfactorily corrected throughout the entire zoom range. U.S. Pat. No. 7,672,062 and U.S. Pat. No. 7,864,443 discuss high-performance zoom lenses that use a glass material having a low refractive index and low dispersion to form a negative lens of a second lens unit so that chromatic aberration of magnification (lateral chromatic aberration) is corrected throughout the entire zoom range.
Recently, image sensors having an extremely large number of pixels have become available; and can be advantageously used in an image pickup apparatus such as a TV camera, a video camera, or a digital still camera. However, in order to optimize the benefits of such image sensors, a zoom lens which can give a high image quality is required. Thus, there is a demand for a zoom lens that has high optical performance in a variety of image pickup apparatuses. Specifically, in the positive lead type zoom lens, it is important to appropriately set the zoom type or the lens configuration of each of the lens units to thereby obtain high optical performance throughout the entire zoom range with a wide angle of view and a high zoom ratio ensured.
In general, it becomes increasingly important to satisfactorily correct various aberrations throughout the entire zoom range to thereby obtain high optical performance throughout the entire zoom range. In particular, it is important to satisfactorily correct chromatic aberration of magnification. Here, as the correction of chromatic aberration of magnification, it is important to satisfactorily correct not only the amount of chromatic aberration of magnification between the C and F lines based on the d line, but also the amount of chromatic aberration of magnification between the g and F lines at the wide-angle end area.
In the positive lead type zoom lens, it is important to appropriately set especially the lens configuration of the second lens unit used for varying magnification to satisfactorily correct chromatic aberration of magnification throughout the entire zoom range with a high zoom ratio ensured. If the lens configuration of the second lens unit used for varying magnification is not appropriately set, it is difficult to obtain a zoom lens that has high optical performance throughout the entire zoom range with a wide angle of view and a high zoom ratio ensured.